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Dr. Cunningham—Surface Anatomy of the Primate Cerebrum. 105

he has supposed that its upper end is gradually pushed backwards until it
assumes a situation and direction which brings it into a line with the fissure
of Rolando. He is therefore obliged to assume "that the frontal lobe of
the cerebrum increases during growth relatively more than the part which
is placed behind the sulcus centralis insula?." We know that this is not
the case, because if it were we should also have the position of the fissure
of Roland affected, and this is almost as stationary and fixed after its first
appearance as the sulcus centralis insulse. But further the Sylvian fossa
has a growth peculiar to itself. The anterior end of the fossa maintains
throughout its entire growth very much the same relative position, whereas
the posterior end extends rapidly backwards. But this backward growth
does not affect the entire area : it seems to be brought about by a continual
backward retreat of the surrounding mantle-wall, so that the position of
the sulci when once they are laid down is not interfered with.

The post-central sulcus is much later in making its appearance. As
a rule it does not show until the middle of the sixth month, or even later.
Its development nearly coincides with that of the intra-parietal sulcus. It
would not be possible for this sulcus to take form at a date mucli earlier
than this, because the ground which it occupies on the insula has hardly been
included within the Sylvian area, at the time when the two other sulci appear.

The period at which the three radial furrows of the insula can be best
studied, in their relations to the corresponding sulci on the surface of the
cerebral mantle, is in the latter part of the seventh month, or the first part
of the eighth month (PI. i., fig. 33, and PI. iv., fig. 1). Still, it is right to
state that exceptional cases are met with, and I have observed foetal brains
which had very nearly reached this stage in which the insula was perfectly
smooth. Further, there is good reason to believe that, in the development
of the sulci and gyri, the right insula is usually in advance of the left, and
also that the process is greatly retarded in the female brain. Rudinger *
has contended that all the convolutions of the cerebrum of the female foetus
are backward in their growth as compared with those in the brain of the
male fcetus. Upon this point I have not been able to satisfy myself, because

Ucber die TJntersclriede der Grosshirnwindungen nach deni Gescblecht beini Foetus und
Neugeborenen. Muucben, 1877.

ROYAL IEISH ACADEMY.—CUNNINGHAM MKMOLRS, NO. Til. [141